There are many known forms of alumina such as alpha, gamma, delta, eta, theta, kappa, and chi all of which are activated except alpha. Such activated aluminas are of commercial importance because of their high surface areas which make them especially useful as catalyst supports. However, these aluminas are usually in powder or particle form and must be dispersed in a liquid medium before they can be applied as a coating over other materials. Dispersing the active forms of alumina is not only difficult but in some cases impossible due to agglomeration of the particles.
Activated aluminas as set forth by Stumpf et al, Industrial and Engineering Chemistry, 42, 1398 (1950) can be prepared in various ways. One method disclosed in U.S. Pat. No. 3,019,080 involves the hydrolysis of aluminum alkoxides in the presence of aqueous ammonia to produce pure alumina of unspecified form.
Another method set forth in U.S. Pat. No. 3,038,784 comprises hydrolyzing an aluminum alcoholate in the presence of hydrogen peroxide at from 0.degree. to 22.degree. C. to form amorphous alumina. Gamma alumina is produced in U.S. Pat. No. 2,749,216 by hydrolyzing aluminum alkoxides at a temperature of 212.degree. to 300.degree. F. In U.S. Pat. No. 2,796,326 aluminum secondary butoxide is hydrolyzed with water at 32.degree. to 70.degree. F. to yield eta alumina. U.S. Pat. No. 3,357,791 discloses the hydrolysis of aluminum alkoxides in the presence of either acid or base to obtain colloidal particles of alpha alumina. All of these methods result in nontransparent, particulate forms of alumina as contrasted to the nonparticulate, transparent, porous form of the present invention.
More recently, Continental Oil Corporation, Ponca City, Oklahoma, developed a dispersed form of alumina marketed under the tradename of DISPAL. When this material is dispersed in an acidic medium, it has a milky appearance and can be dehydrated at about 500.degree. C. to gamma alumina with a surface area of 320 square meters per gram. However, this dispersed product has a much larger particle or agglomerate size and cannot be converted by heat to the transparent, nonparticulate, porous alumina now claimed.